Transmission delay measuring system



NOV. 3, 1931. H NYQUIST TRANSMISSION DELAY MEASURING SYSTEM 3 Sheets-Sheet 1 Filed May 6, 1930 QOOOOOOO BY E/ Qquzl ATTORNEY Nov. 3, 193.1. H. NYQuls'r 1,829,838

TRANSMISSION DELAY MEASURING SYSTEM Filed May e, 1930 s sheets-sheet 2 l a 47 'evensz'ifzy .57 May mmm@ ommfato" 5 v0j l 20 Commutatw-Segments,.Some/Yeszlstamces connected to 2 Seg/nenas.

.EEE mmmmmm Cammatol' 67 20 Segments/ l ATTOR N EY Nov,l 3, 1931. l H. NYQuls-r l TRANSMISSION DELAY MEASURING SYSTEM Filed May 6, 1930 3 Sheets-Sheet 3 AWORNEY las r riencefhas shown' thatthe .arrangementtherein described gives i staed- Nov; s; 1931 iii-I1fialiautii,k 4Jansma:.As'siefrr'oe'1ro AMERICAN vr''rieurHerm f `AmirEnncrieari'l eeMPAzNY, LA conronnrroiv or NEW YORK TRANS-MISSION DELAY Muscatine SYSTEM .Application yLled Mayv` 16,

i 'l This invention rela-testo :transmissiontdelay l niieasurimg; systems, land particularly; to

I In the patent toNyquistNo.1,645,618thaltr o issued on` October y18, y19.2f7is idescr-linedav f. Y method for,:measuring transmission .delay 19 ali-method andmeans or measuring .Y-such def` lay at yery low -frequencies, as of thejfforder' 0f lO'CyGes 110er Secondes wellrfasfat high trequencies. Y o e l i that consistsl in modulating an input `current of, known :frequency loyjanothercurrent of Very,` low ztreq'uency, ltransmittinggthe Smoduy flated current fthroughga'- system '.c'apableof ik Y 'producing ga- :delay nthetransrnission ,of

such -v current, ialso transmittingl through .an-I` f other channel the low frequency current, de'

7' Ytestingthe low frequencyjenvelopefof the modulated current, knieasuring fthe phase Y fflditference 'between lthe "detecte'dicurrent and f l^vaai ,the low a frequency currentl'as f transmitted I and j determining from l the phase difference 1 tlzieldelayin[transmissionA in ,iu-nits of time." fr While the principle alpen whichthat method Y to is based ais 'applieablefto fthe measurement `of llow as welll'as. high; frequencies, expe-i thefmost satisfactory resuits abovey 250cycles per second;v p The present"inventionresides-.in a method and means, thatv'whfile capable fof :me'asuring accurately the :transmission delay v pro- 1 duced vhy a network `upon.high.frequencies,

isjat thesame time, well adapted for measuring delay llat Very low frequencies, ,for example of 'the orderrof v1.() `cycles per second. fVV The vinvention will be clearly understood from the i following description when read in A "conection'with the zattached `drzmfings kof 'Y wliieh'ligure vl Shows schematically A'the eine l bodiinei'it of the invention in a, very' .simple thepurpose ofwhich is ito :describe .the

, 'underlying principle4 of the .irwentiongL 2 and 3., when arrangedsoithatthe numbered Vconductors V,thosefigures are yin limitarl show thev circuit Ycomiections inYdeta-il v of almeasuringset embodyingthe invention-5 mig- 4 is a 'flagmentai-rlsketch illustrate' j in-gtheadescriptioneta testlempfloyed inoperatinfi the fmeasurin "set," 1

1930. sxria1-im. 450,223.

bolcally any source capable fof generating oscillations of frequencies yranging upwards :from'alowerlimit-oi' l0 cyclesror lessup w25 cyclesv4 or ancre. .The ,generator is connected withthe reversingy switch through the n'etwork 22 the purpose yof which is to make 'the 'impedance of 'the `source of oscillations when 'loolzedgIl-to from the switchcontacts equal toav predetermined value such, for example, as I12(Kltlloh1ns..y The switch 23 is connected between-the .network 22-andthie potentiometer 241;,tliat-.isfmade upofa plurality rof resistancesf 'commutatm'l comprising Aa vpluralitynf segments numbered-l to20, is connectedvto the potentiometer 24. The potentiometer24c isdividedintoja plurality' of sections .such zas25, ,'26 and the' taps ,from the junction pointstof successive sectionsare connected with vpairs-o segments oi' the'commuvtator. Eer exampld-,thetap .from the junction .offfisections v2,5 and .f2.6 is connected with segments Zand 20 so that the Voltage across `V se'ction25 will befapplied to the transformer 28i whenever the vlorush ,29 'rests upon segment 2forsegment 20, which segments are strapped targether.7 .Itwi-ll -accordinglylbe seen that as the brush 29 moves lover the segments inthe vQdirecticm represented Yby the arrow, 'the voltage applied to the primary of transformer l28 wil-'L frise,l lileaching a lmaximum when the 1go' brush y reaches esegment 4ll and will thendiminish by steps, reaching zero when [the the lbrush again .rests upon segment l.. .The action of the commutator `is 'to modulate the currentof the frequency f generated by the g5 oscillator ,21, K the modulating 'frequency .5 depending itpon the rateofrot'ation of the brush 29 over thesegments of the fcommutator. As has beenLshown, thecommutator creates -o'nelifa-lf .of the-modulated'wave during one revolution` of the ,brush 29.4 By throwing the reversingY'sWi-tch to its opposite position, while the brushispassing over segment 1,'the other half ofthe-modulated wave may be created duringthefsubsequent revolution of the said 95 brush. j It ,willaccordingly be #seen that 'by they operation fofthe switch y23 during two revolutions ofthe `brush '29, a :com-plete modulated wave .isproduced .Y

j Inthe.practical embodiment :of nvchf 1W produced tion, as shown in Figs.r2 and 3, which will later be'described fully, the commutator employed is that of a'multiplex telegraph dis-f tributor, lthe lowest speed of which is 2.5

revolutions per second. That arrangement producesa 1.215-cycle wave, so that the bands by the modulating action may be represented by f -l- 1.25 mdf-1.25 cycles per v s second.V Thesecondary winding of transformer28 'is connected with two bladesof the four-blade switch `,30, the other two=V blades yof which lare connected with they primary ofv transformerV 31.."llhe` upper `contacts of switch 30 vare connected in suchmanner that sides ofthe-detector-tubes 32, 33 the plates of which are connected with the source of potential 34,*having inV series therewith a resistance Y vof theorder 'of14800 ohms. Y circuit of-the detector-is connected with the Y 3o The output brush 36of coinnfnitator No.2 and also .with the' midpoint of thefpotentioineter The. connection with thebrush36 includes the resistance- 38 which isof the order fof4800 vohms and also' the condenser 39.v As in the caselof commutator"No.j`1,'the` pairs of yseg- Y L ments of commutator No. 2 are connected to-, gether yand 'those pairs arev connected 'across 'portions 'of-the potentiometer 371 The ciently sluggish yasto respond onlyfto the direct current component of 'the detecting ioperation, that is effected'byithe commuta'torV and its `associated potentiometer v,The brushes -29 and 36 of the-two'commutators v are arranged to rotate togetherfbut'the ar- Y rangement is such that one of the brushes, for

- Y 'example 29,'may be shifted at will to'l alter the phase'angle that it makes with brush 36. v

VThe manner .inwhichj the system works tomeasure the kdelayintroduced bythe network 41 in thetransmissionof a `vlow frequency- -wave therethrough'willnow be de# scribed. Letit be assumedthat the oscillator 21'isV generating aflow Vfrequencywave of the order. 'of' 10 cycles. That wave will be impressedacross -thelpotentiometer/24 and it v'will be :fullyz modulatedfby the movement of thebrush 29 over-the commutator No. 1 `and bythe:manipulation` of theswit'ch 23..-V The modulatedlwave generated vby the commuv -tatorgand 'thev potentiometerv 1s theoretically sine wave of .1.25y cycles except for-the presence of lcertain* harmonics,Vv such Aas the 19th.1j21st, .39th,V 41st,@ etc., which harmonics Y. was@ tional to sin (27r2.5`tl 6) and the wave gener-l .vate'dgby commutator' 2 be proportional to sin Vgalvanometer is bridged across the potentif ometer. That galvanometer should be suffi-V reads zero.

are small enough to be neglected. Those harmonics arise from the fact that the wave produced by thelcommutatingdevice is a stepped wave, although it follows the sin-e form. The sidebands of modulation, namely f+1.25 and 7 1.25, are impressedby the transformer 28 upony the circuitiV containing the switch 30, which switch should'at the outset be in its upper position so that the waves will be impressed directly :upon theldetectors 32, Thetwo frequencies f+ 1.25 and f1.25 are converted by the detector into 2.5 cycles and also a number of higher frequencies1-thel latterihaving no appreciable effect on 'the galvanometer on account of itsv largeJ damping winding. Y V'It will be; seen thatwhen a voltage is applied across the conductors 43, 44, the-com- 'mutating device No. 2causes`a=full wave to be'gener'atedk for eachy revolution of the brush. In the p-resent assumed case, a voltage of 2.5 cycles would be generated, since the shaft to which the brush"36 is connected operates at 2.5'revoluti`ons per-second. Since the output ofthedetectorf32, 33 is a 2.5-cycle wave, the faction of thecommutating device No. 2

upongthe-phase angle between-the brushes serenata r` The-manner in which Vthe commutating dei vice Nol`2`op'er`ates is -asfollow's'z Let thev wavey coming'from the detector 32-'33fbe propor. 5

Y27r2.57), wh ere His an angledependi'ngon the setting' of vthe brush 29 fwhich* may be rotated upon its-shaftwithV respect to'brush 36,rotated the same shaft. Since the wavev generatedf 5 byv commutator #2 completely modulates the detector output, we have a cur-r rent flowing` through the galvanometer 40; which'is,proportional'to J sinl (2132.525) sin (2r2.5t+0)=1 l' 'v v 1/2 cos (21%57140) -l-l cos (-0) The five-cycle'componenthas no appreciableleffect on thegalvanometer, but the cl-0.

component, lf2 cos y(-,0),Vca'uses"a deflection except where) is v or2700, whenthemeter t Theiphase angle between thebrushes l297 and 36 of the two 'commutating devices is 40 lreads fz'ero, although zeroreading `is ynot necessaryv lif the network 41 ,has no kampliiication'or attenuation. The switch" 30y is thenthrown toits. downward position, therepreferablyadjusted so that the galvanometer by 'connecting intofthel circuit the network l 41`,Qwhose ldelaying effect upon the signal' 'wave'flis tofbe determined. The brush 29 is then ,shifted'upon-thefaxis on which it rotatejs"toa-suchextent as'to produce the same s resultant upon the galvanometer 40. The difference 'between thephase angle then ,existing together-being indicated byl-numerals;Y :The I the pha's'e'- angle; between those lbrushes when r`the'switcl-i 30' wasI inits upper-position, viz.

f6`,-"isa n1 Vindication ofthe delayf-introduced the transmission of' thegmodulated signal' l `by 'the network 41. That angular delaymay bei translatedintofunits of time inthe fol"- lowing manner. Since 'in the assumed case the shaft carryingfthe' brushes '29 and. V36' rotates-,one revolution in V0.4 second,and since e there are 3600*in1 a? revolution,10,V shift of' 'the brush 'correspondsto 0.4/36O=.00111secV ond/delay. -That tigureimultiplied bythe number of degreesditference betweenthe vphase angles, shows thetiimeY delay ,introducedk by the network 41i'n'the' transmission of the 'fsign'alfof the frequency fv'generated by 21 VAas modulated by 'thecom-mutating device No.

l1 wh-oseffrequency is 1.25 cycles per second. 'In lthe arrangement shown 1n Figs; 2and lthelsame numeralshave been employedfto 4imii'cate parts similar toalliigures.,` Thus, the oscillator 21:, having V an impedance of" 600fohms, is connected with the vpad 22 comprising a plurality ofre's'istances such that l *the combinedresistance-lookinginto the net- Y workfrom "the lright. .thereof Vis 1200 ohms.

The terminals ofthe .network are connected with'rth'e vcontactslof the reversing relay 45` that serves the same-purpose as the reversing yswitch 23 of FigJl; The reversingrelay 45 f. is l'connected by conductors4 46 and-47with *.tlie system of the controlling relays shown in e Fig.13,xoonductor46 being connectedV with .the-right-.hand vcontact vof relay `48 and coni ductors47 :being connectedfto ground. LThe armatures ofrelay 45 are connected with the y outer terminalsof the .resistance network ofl the potentiometer v24;, which 4network com- .prises -a plurality of`r resist'an'ce's` fconnected with the segmentsor'pairs of segmentso'f the commutating'device-- No.1. ,That'lcomm'utat- 'Qing device `includesa segmental ringy conf ftainingi20 segmentsitof which only 11 have been shown) ,the lpairs of,segmentsfconnected Vjcommutating devicewalsoincludes the continuous ring 49 and agbrush 50 fthatsweeps over the segmental, ringand the continuous ring so as ,to eifectively transmit to Athe-detec- 'tor 32-33 voltages determined by the posi-- tionfof the brushfOnpon` the segmental ring.

The segments 51 :and 52- fand; the ring :53,

:together vwith Athe brush 54, serveto `control the operation of the :reversing relay 45. The

' segment 51 is connected by conductor 55w1ith f the left-hand windingof -control'relay 56.

.Thesegment'52 lis `connected lby conductor '57 llwith ,the armature and the rightfhand windconductor 58 ing'ofrelay 56. Theiringf53 is connectedfby .withfonesidey of the condenser Y 559er Fig; s. f

I The :eommutating deviceN o. l is aconnected Y Awit'hthe switch 3 0whicl1, when A'thrown .infits n c5V :upper :positionfs'ervesgto connect they com -3-.pole switch 63, of which two ofthe blades its'ar'mature touches either of its contact kpoints,for example, the left-hand one. vCurrent will 'accordingly flow from thebattery `65lthroughthe left-hand Contact, the-rightmuta-tor with theh variableV artificial line 60,y and thereby with the primary windingof transformer31,iwhose secondary is connected n with the input-of the detector 32,-33. The

switch 301m its lower position connects into `the circuitthe network 41producingthe unknowndelay.. The output of the saiddetec- Ht'or is connected with the commutating device No.r 2 comprising a segmental ring containing 20 segments, a continuous ring 61, and a brush '62 that is-arranged to sweep over the said-rings. The potentiometer 37 is connected with two of the leftfhand contacts of the f Y The manner in which the circuit of Figs. Y

2 and 3 operates isas follows: Let it be assumed that relay 56 of F ig. 3 is jarredsothat handwinding of relay 56, both windings of relay. 48 to ground, energizing both relays,(.;)5 :and thereby causing the armature of relay 56 toV be held against its left-hand contact vand atithe Sametime moving the armature ofrevlafy48 onfits left-hand contact and holding it there. Let itibe assumed that, at this :in-Q00 etant, brush 54'lias-fmoved onto segment 51 `and ring 53, vand that brush 50 has moved onto Vsegment l1 and ring 49 vas shown in Fig. .2. Thefconnecting of segment 51 'and ring -53`by..the brush 54 establishes acirouit that` ,105 Y may bev traced fromtheungrounded side of condenserf59 (see Fig. 3), over conductor58, ring A53, brush 54,. segment 5l, conductor .55,

left hand winding ofrelay 56 to,ground,'but 1 since therek is no charge on the condenser, vnoV17 f,110

eifect isproduced upon relay 56. Atthis instant relay45 is deenergized,an d we will -assume that-its armatures rest upon the lleft `hand contacts 66 and 67.Vv 4The oscillator 21 vwill accordingly impress a voltage wave of.115

frequency f across potentiometer 24. The Y brush 50, starting from segment l, will sweep over allof the .segments in succession, and return aga-in to segment 1, causing thereby the production of a half cycle of aI modulated-,120

wave, representing the modulation vof fre-A quency f by the frequency of the commutator. During the time in which the .brush 50 is moving over segments 11to 10 inclusive the v-brush54 moves over segment `51, and passes ,125

onto ysegment 52fwhen brush 50 reaches seg#y ment 1:1. rush 54 thereupon connects segment 52 .and ring 53 and establishesacir- .cuit including battery 65,leftvh'and Contact -;df,relay,5,6 conductor 57., segmentV 52, brush 330 Brush-54 Ywillcontinue toV travel over seg.-

ment twhilebrush 50 is passing over segmentsV 11` to 2O."y When brush '54'l'eaves seg- 'mentf52,-the circuit of condenser 59 will be gopened, l'and as' soonras .brush 5 4 'passes'ontosegment 51, the said condenser will discharge through a. path` including conductor 58, ring 53,brush 54, segment 51,'conductor 55 and, the 'left lhand-winding of rela-y 56, thereby causingthe armature of that relay to move to its right hand contact. *That connects the negativebattery 7 3 to the` armature ofrelay 56, and thereby reverses the current through,relay 48," causing its armatureto touchffits right handL contact.. Thereupon,

lbattery 72 is connected by conductor 46 .with reversing relay 45, and as the result thereof the armatures of that relay are moved to the right hand contacts. By'thisftime, brush 50 will have moved onto segment 1 and the comother mutating system is ready to produce the half cycle of' the modulated wave. It is desirable to point out that brush. 54 is slight- Y ly in advance of brush 5'Oin order toenable the controlrelays l56 and 48 to ybring about l the operation lof reversing relay 45, 'sothat onto segment 1.

the oscillator 21 will be properly connected -with the potentiometer 24V for the generation of the next half cycle, when brushtO vpasses Brushes54 and 50`will continue rotation battery 73,:l the circuit including they-said battery, right hand contact of relay .56, con-A c ductor 57, lsegment 52, brush 54, ring 53,7 con-V is thus ready'to cause the operation of relays 56 and 46, and thereby bring aboutthe opera-l tionof'reversing relay 45 as soon as the brush 54 'again moves onto segment 51."

The operations just described vproduce waves of frequency f freely modulated by the commutator of al frequency of* 1.25 cycles.

' That wave will be impressedby the'switch 30 upon the transformer 31, the' switch being in its upward, Calibrating position. vSince the vapparatusshown is designed to matchlines and apparatus of 600 ohms impedance, a 600v ohm variable artificial line is used to regulate..

-thecurrent amplitude at the input to the detector. VWhen the switch 63 isthrown to the right there will be connected across f the primary of transformer 31 the thermocoupley V64 and the 'resistanceV 68. When the switch 63 is thrown to the left the resistance 69 of 600 ohms is connected .across said transformer-- The artificial line 6() is adjusted so .that the l same current is used at allV frequencies. `Whenit is desired to send one milliwatt into 'theunknown delay network 41, the' oscillator les should lgive approximately 14 ab above one .nilliwatt', since that is the loss measuredbeieee-,eas

#switch 30 inits upward positionand Vswitch 63"'toj the might.` ;k The' same deection is obt V.tained withsthev switch 30 downward'when the' Vloss 'inthe'artificial' line* is decreased by Van amount `equal to the loss in the unknown delay network. While it is desirable to maintainl thecurrent at the input .tothe detector constant to avoid fpepeects in the detector, it is not desirableto use such a high current Vat this point when measuring withk switch 63 thrown to the left since the amplification given by the detector will permit interfering yfrequencies to aect-the galvanometer unless anadditionall() TU loss is inserted in the artificial line when theswitch 63 is moved f from right'to left.,`A` It is desirable to compare Athe currents.V at thev detector inputY for .the '..c'alibrating and VYmeasuring Vpositions of switch 30 to make sure that they are nearly ythe same value, using highercurrent strength lto read the galvanometer more easily and then introducing the l10 TU lossv to avoid the effect Zofinterfering frequencies.

. The two frequencies f+125 /f-V125 are' kconverted by :the detector. '32,- 33y into r21.5 cycles and 'a number of higher frequencies, `'which latter have no appreciable eecton the ,Y Y galvan'ometer on-account of itslargedamping .andV when brush `54 passes onto segment V52 vrthe condenserv 5,91wilfl again be charged .by

windings; rlhe provision of afiilter 72with .the battery 34 protects'the circuit from batteryV noises. rThe 2.5-cycle current impressed across fthe cominutating devicelNo. l2 will be ldetected therebyfand the direct current resulting therefrom'will be impressed upon .the

galvanometer 'when the 'switch` 63 is in its left-handposition.V Y c The manner in which the commutating device-No.2 operates has been fully described inconnection with Fig. 1,and need not be completely stated again- As previously men-l tioned-,the current flowing' through the gal vanometer, when switch 63 fisthrown to the left is proportional to f f .i sin (21r2.5t)sin (2n-25H5):

t -11/2 @siamo +1/2 cos 40) `'The `five-cycle component has no appreciableeffect on the galvanometer but the d-c f component, 1/2 'cos 6), causes a deflection except where 6-1s'-90f or?? 00, when the meter reads Zero; Y v

The ineasurementof delay consists `of tal;-

ing the dilference'between the twor settings 0i land 62 of thebrushes'whichare necessary to produce zero reading'of the' g'alva'nometer,` 'with'and' withoutthe unknown delay in the lcircuit.v Since the motor rotates one revolutionfin 0.4 second, and sincethere are `360"in airevolution', one degree shift ofthe brushes ,f corresponds Y toA 0.4/360'=.0O 111Vv second genc "en thephase di-iernce, it, will, ef course, lbe; ,un-,-`

yderstccdf thaejtherelative -pesitionr ofthe brushes'may be xed1y;maintained andtheA ft phase ang-le may be measured-.by rotating; the segmental commutatingirings;

lietjarrangement shown ten.diedate adjust;y thef-relati-yepositionsbt the"brushesf 5,0' andi 54; in slider; Vto;elimina-te' l the'ei'ect upon the reversingnelay-A ofthe y time la-glinathe,v eperaticn; ei-ffthe, ciontrc'l ne' j lays; It has; been peint-,ed routl hereinnleefere; Y that; brushr 54 .is normally-'positioned f t0n, bev

in advance offbrush `50 inonder to, bring l 2f?? abeut-:the operatien. ctv-,the control A,relays v and: of: the reversing- :relaiyE ;fs0.that;theoscillator 2L will be: properly connected-withtheV potentiometer;'2e-When the bnush- 50 is;

on; segment 1, VTol,effect the proper atl-juste.

`5ml-mentetV 'brushes 50- and 54:v the oscillator-f 21;

- and the-pad-ZEZ anediscennected trcm-tliecon- Y' tacts offrelay 45; and ai source of direct.:cur-rV irent,-preterabl-yv a lgyveltbattery, is con# the; pot entiemeter andA areccnnectedwiftlr the ind-uctance74ev and? the; condenser 75, the latter serving' asa spank-killer: I'I-hcse resists? Vusi-ng the contact point V-)yafnd .one sideeff' the inductance-.Tt-,the other. sideofwhich is lconnected with the conti-n neus.;,ringed-9;Refk

lay 455.-.- is connectedwiththecontrel system shown Figs. 2 l t ff' ,r

Assumingthat the brushes arerotating,refl

I lay- 45 Wil-Lebe: operatedy each-.time the-brush -moaies onto; segments-5l,.- Assuming .for example, that the armatures of 45,. are moved:` 'ce-the; left as,-N the@Y result-'of the passingcf theabrush f 54 fonte@ segment 5.1-, current will flow j throught the indu'c'tance coil 74 and; a, f voltage will be established acressit. 1fat nu' Y, that instant. the yconltaet pzoi-nt 7f3- viseheld against segment. Lef-'that zcemmutator, and no current flows through the teleplroneIres ceiyenii ,eicliicks-fare not heard, it Will' be evident that brushes 54 and 50 are not prop- A erly adjusted,since brush is not upon segment 1; Thereupon the Contact point `7 6 connected with the telephone receiver vWill be' '.f?. moved from segmenti toV segment 20 in order to determine vWhether,brush 50 is on the jlatter segment at the instant the armatures were moved to their contacts. If a click is 1w heardin the telephone receiver when the lContact rests upon segment 2O it indicates that netted-with the saidcontacts.` V'Ehe; arma-g tures.I @1f-.relay 45? are j-alse disconnectedrem ancesfof thepctentioineter; 24; that normally ,i are connected .Wit-lr segments-20, lr and 2 are;-

Bruschi-50;wiaeccrdinglybe moved and fun.. ther; tests` will be made todetermine Whether the adjustment has-been' suflicientto cause brushg() to-beon; segmenty l' when the armar tures of: Relay-45 liavemoued to--theircontact points, Ifa-fter the adjustment has-*the madeno clicks are heard thetelephone receiver when thecontact point yis placed againstsegments 20fand2, as the brush sweeps .7: Over-the segments, ity indicates that brushes,

50 and:v 5.4i have been properlyadjustedf It isi teI be; understood that while ther inventienhasybeen disclosed; as embodied in particular forms and arrangements, the in;-` uentieng-isi capable of embodiment in other and` different forms, Withput-departing from the spirit and scopeI ofthe appendedL c1aims.

Whatisclaimed is: if li.' In-y a-j transmission; delay measuring system,the methodthat consists in modulating awave of known frequency by a different frequency transmitting the side-bands of suchmedulation over a medium capable of preduc-ing.- substantially 'no delay in transmission-,beating together-the said side bands,- detectingl thatv frequency that is double the said` difference frequency by'vvhich the orig-- in al Wave- Waslmodulated, measuring the direct-#current resultant', of the said. detecting step,; .then transmitting-the said side-bands over a-mediumgpreduc-inna measurable delay, beating togetherthe side-bands and detecting the said double frequency, adjust/ine*y thephaseyangleet the last detectingv step to give thesame direct current resultant as is given when transmission-isefectedioverthe medium' producing-no delay, and'measuringythe' said phase'angle. f

2; In a transmission delay. measuring system, theymethod thatconsistsy ina modulating a. Wavey of-known frequency by a different frequency, transmitting'- the sideebands of modul-ation overfavmedium capable of preducing.- substantially noy delay in transmission, bea-tinge;` together thesaid side-bands, detect ingthat frequency that is double-the said' differenty frequency by' which the original Wave was modulated measuringthe-directcurrent resultant of the said-detecting step,y adjusting thefphase angle 0 of detection untilY zere direct. current is indicatedthen trans- ,Inittingy 'the said side-bands overy a. medi-um .producing a-l measurable delay, beating-fte,-

gether thosezsideffbands. and detectingxthesaid double frequency, adjustingr the phase angle. e. the last detecting stepy to givej zero direct'current resultant,4 and measuring the `diierence between the said-` phase angles` 0 yand 0L" l, y

. 3,. I atransmission delay measuring system; the; combin ation-With a source of -Wavesof'knovvny freqiiencyY of means to rfully modulatev thesaid ,Waves at a finedr rrfrequency diftering from vthe'said known frequency, ay

' transmitting Ine-diem,"capableY of prodiueingA substantially no delay,`{upon which the side# means to'detect that resultantof the beating operationwhose frequency is double the said Y 'xedffrequency, a'device to indicate the mag` nitude of the detected double frequency current,.a'second transmitting medium capable of introducing a measurableV delay, and

switching means to connect the second transmitting medium between "the'said modulating meansand thesaid beating means in sub- I stitution lfor thesaid vfirst transmitting mejdium.V Y'

- 14. In a transmission delayvmeasuring system,y thecombination with asourcev of oscillationsV of a; potentiometer upon which fthe said oscillations are impressed', a commutator comnrising a. segmental ring and a brush capable of rotating thereover, the segments be-Y Aingso connected with thesaid potentiometer that Qthe said oscillations will be moduiate'd by the rotation of the said brush,fa network sc connected withthe said commutator that the modulated' oscillations kwill 'be impressed thereon, a detector Vconnected with lthe network to detect thecurrent of the frequency at which the brush rotates, asecond commutator 'alsov Acomprising a vsegmental ring. anda brush rotating thereover, a second potentiometer connected; withthesaid second commutator, means to connect the output of the said detector' between ythe brush of the second commutator and the midpoint ofthe second potentiometer and a galvanoineter bridgedV across the said ysecond commutator'.

- 5.'In aitransmission delay measuring system, the combination with a source ofoscillations of a source of low'frequencyfvaliations tomodulate completely the ,saido'sciL lations thereby producing two side-bands, a path producing'substantially no delay in transmission, a) second pat-h capable-of producing a finite delay'td be determined, switching means adapted to applythe modufj lated oscillations Ato either path. `a detecter radapted for Yconnection witheither path to beat together thesaid side-bands toy produce a wave of double thefrequency ofthe said variations, means to produce a direct currentresultant fromthe saidwave of double frequency, ,an indicating device to showY the magnitudeof the said' direct current, and

means to lindicate the phase difference produced by the transmission overthe two paths.'l

Y 6.Y Ina-transmission delay measuring sys;

tem, the-comb inat ion witha source of oscil- A; latlons of known frequency variableV atfifvill, i

of a potentiometer made up of a plurality of sections, a reversingrelay adapted to consaid potentiometer, abrush.adaptedi to rotate "over the said commutator to modulatethe saidoscillations, a path having substan-. tially no delay upon whichthe Aside-bands of tem,the combination with a source of oscili lations of a potentiometer comprising al plurality' of sections, a reversing' relay connectmgthe said source* to the said :potenvtiometeradapted by its operation to change the phase of the oscillations impressedupon the potentiometer through the contacts of said relay, a commutating device connected withthe 'sections of the potentiometer to modulatethe said oscillations by varia-tions ofva diiferent frequency` a transmitting medium upon which the side-bands of modulation are impressed, the said medium being capable'of producing afinite delay, means to beat together the said side-bands, means to detect that-resultant of the beating operation whose frequency is double that of lthe said variations, an indicating device upon which thel direct current vresultant `ofthe saidy double frequency may be impressed, and switching meansadanted tov controlthe said reversing relay whereby the connectionsy betweenthe said source'and the said poten-` tiometerl will be reversed after-each cycle of the said-commutator,`k f y l'8.' Ina vsignal delay measuring system, the combination with a transducer of means to send vcarrier current modulated by low frequency current through the said transducer, means' connected with the transducer outputV to detectA theresultant,` whose frequency isy double thatv of the low frequency current, and meansto make phase compari,- son between the double Vfrequency resultantk andthe lovt7 frequency current.

In testimony whereof,I haveV signed-my name to this specification this f5th` day of May1930. l

' VjfHARRY,NYQUIST"Ig neetvthe said source. withthesaid potentiom-V eter and to reverse thep'haseofjthe oscillations thusapplied, afcommutator havingjts segmentsy connectedYwith the sections ofthe 

